This invention relates to a marine propeller.
In the past propellers have suffered from a loss of efficiency towards the outer edges of the propeller blades where water tends to be flung outwardly from the blades as a result of centrifugal action. The rotational energy of the blade is thus partly dissipated in driving water in a direction other than parallel to the central axis of the propeller.
The object of the present invention is to go some way towards overcoming the above disadvantage.
Various ring propellers have been attempted earlier, but none of these have been very successful. Examples may be seen in British Patent Specification Nos. 203/1879 (Fisher), 15045/1890 (Jensen), 453/1893 (Rateau), 16750/1912 (Allen), 147705 (de Coninck), 192908 (Seay), 780910 (Taylor & Shipp) and 1324356 (lips N.V.). In none of these do the propeller blades have parallel edges and a constant cross-section along their length, which is a major distinguishing feature of the present invention and which enables the propeller of the present invention to operate more efficiently than any of those mentioned. British Patent Specification 2000477A (General Motors Corporation) shows a ring fan with parallel edges on it on its blades, but the blades do not extend as far as the ring, and the shape of the ring as well as the manner in which the ring is attached to the blades render it quite unsuitable for use as a marine propeller.